A proportional modular valve, with an axially displaceable control piston and a travel sensor for the control piston, is manufactured by the Mannesmann Rexroth Aktiengesellscaft, and is commercially available under the reference 3WRC. Such valves preferably adjust the volume of hydraulic oil flows, for instance with forging equipment, power press cylinders, dye casting machinery and the like.
These valves are characterized by simple construction, because the travel sensor by virtue of its pressure-tight construction can be mounted directly in the passage of the valve housing. The directional transmitter rod extends out of the valve housing interior chamber and into the opening of the travel sensor tube. Since with this type of structure the user pressure prevailing in the passage is also effective in the pressure-tight travel sensor tube, the danger exists that, in cases wherein high pressure peaks with steep gradient sides occur in the user pressure, plastic bulging or expanding of the pressure-tight travel sensor tube can occur. This frequently leads to disturbances in position detection, especially in the case of the use of inductive travel sensors with coil bodies positioned on the travel sensor tube. The winding can tear, leading to breakdown of the associated control electronics, and with that the breakdown of the valve.